patch 9.0.1544: recent glibc marks sigset() as a deprecated
Problem: Recent glibc marks sigset() as a deprecated.
Solution: Use sigaction() in mch_signal() if possible. (Ozaki Kiichi,
closes #12373)
diff --git a/src/proto/os_unix.pro b/src/proto/os_unix.pro
index 9266364..c3a8483 100644
--- a/src/proto/os_unix.pro
+++ b/src/proto/os_unix.pro
@@ -1,4 +1,5 @@
/* os_unix.c */
+sighandler_T mch_signal(int sig, sighandler_T func);
int mch_chdir(char *path);
void mch_write(char_u *s, int len);
int mch_inchar(char_u *buf, int maxlen, long wtime, int tb_change_cnt);